Patent GB-582419-A (GB)
Title: Improvements in or relating to radio-location apparatus
IPC: G01S13/44
Filed: 1943-06-30
Abstract: 582,419. Radiolocation; wave guides; pulse generating circuits. COCKCROFT, J. D., ASHMEAD, J., COOP, E., KEMPTON, A. E., FORSYTH, P. G., and NEWSAM, B. June 30, 1943, No. 10653. [Class 40 (v)] In a radiolocation system, particularly for locating surface ships at sea, the echo signals are fed to the receiver through a wave guide 7, Fig. 1, having forked ends 8, 9 terminating in the focal plane of the reflector 2 at equal distances from the focus, the two forks of the wave-guide being alternately switched into circuit with the receiver 14, 15, 16 the output of which is presented against a spiral time-base on a cathode-ray tube 19 to indicate the range of the target and also against a linear time-base on a second tube 22 to indicate its angle of bearing. Each fork of the guide contains one or more gas-filled discharge tubes 10, 11, 12, 13 which are periodically triggered to allow signals to pass through the two forks in rapid alternation to the receiver to appear on separate traces on the bearing indicator. The bearing is determined by rotating the reflector in azimuth until equality of the amplitude of the two .traces is obtained. Fig. 1 is a block diagram of the installation. A pulse generator 4 controls the transmitting oscillator 5 through a series modulator 6. The echo signals received by the wave-guide 7 pass via a heterodyne stage 14, 15 to receiver 16, and thence (1) via amplifier 18 to the modulating plate of the range indicator 19, and (2) via amplifier 21 to a Y-plate of the bearing indicator 22. Pulses are fed from generator 4 to a master relay set 24 controlling (1) the spiral time-base 25 of the range indicator 19, (2) the linear time-base 26 of the bearing indicator, (3) a multi-vibrator unit 27 generating the switching-pulses for the neon lamps in the wave-guide 7, (4) a signal selecting or " strobing " unit 28 which generates impulses applied to the control grids of both indicators to brighten the echo trace it is desired to select, so as to correlate the observations made on the two tubes. The unit 27 also generates impulses at half the pulsing frequency which are applied as a shift voltage to the X-plates of the bearing tube so that successive echo signals appear on separate traces to facilitate comparison.' Other pulses generated by unit 28 are applied to an automatic gain control circuit 29 so as to control the gain of the selected signal only. A calibrating unit 30 provides marking " pips " representing 1000 or 10,000 yard intervals, which are applied via switches 17, 20, 31 to the indicators 19, 22 and relay unit 24 in place of the echo signals. Wave-guides and feeders therefor. The wave-guides are provided with neon lamps as described above, and are brought over the top of the reflector down to the focal point in a series of right-angled turns, Figs. 2 (a, b, c) (not shown). The transmitting and receiving wave-guides 3, 7, Fig. 3, are coupled to co-axial channels of an intermediate feeder having a junction box 35 to permit relative movement. The intermediate section of the feeder comprises three co-axial conductors 36, 37, 40 (see also Fig. 3a) of which 36 and 40 are separated at the junction by gaps, which are shunted by open-ended quarter-wave co-axial lines to prevent leakage of energy, and the adjacent ends of the third conductor 37 overlap to form a rubbing contact, so as to isolate the inner from the outer channel. Circuits corresponding to the block diagram of Fig. 1 are shown in detail in Figs. 4, 5. The following features are selected for abridgement. Spiral time-base circuit for range indicator (see unit 25, Fig. 4). The spiral time-base is generated by periodically shock-exciting a resonant circuit 83, 85 which is included in the cathode lead of one of a pair of valves 80, 81 and is shunted by a resistance 87 in the cathode lead of the other, the resonant circuit including an inductance 85, which acts as a deflecting coil for the C.R. tube, and a condenser 83 the voltage across which is applied to one pair of deflecting plates. The instant of the shock excitation is determined by an impulse from the master relay unit applied to the valve 79, the pitch or decrement of the spiral is determined by manually varying the feed-back applied to the resonant circuit through a channel including valves 88, 90 and diode 91, and the maximum radius of the spiral is determined by limiting the current passing through the diode 91. Rectifier for echo signals of intermediate frequency. The output of the amplifiers 49, Fig. 4, is applied through a filter circuit 50, 51, 52 to diodes 53, 54 the resulting load current being tapped off the mid-point of winding 50 and applied to the grid of valve 55. Signal selector circuit 28, Fig. 5. This generates a " strobing " voltage, which under manual control is timed to coincide with a selected signal to distinguish it from others on the two indicators. For this purpose, a pulse from valve 72 of the master relay 24 is applied to the grid of the valve 74, thereby causing condenser 106 to charge through resistances 107, 108, thereby generating a saw-tooth voltage which is applied to the grid of a valve 109, the cathode of which has its bias determined by resistance 110. By adjusting this resistance, the instant at which the valve 109 becomes conductive can be made to coincide with the position on the range time-base of any selected signal. The resulting impulses are fed through limiting amplifiers 111, 112 and emerge as a' series of square-shaped pulses which are transferred through a differentiating circuit 113, 114 to the grid of valve 115 and thence to the grid of valve 117 coupled through a common cathode load to a valve 118, the grid of which receives pulses from valve 75 of the master relay. The output voltage produced by this dual control consists of a square-shaped pulse on which the signal selecting pulse released by valve 109 is superposed. It is fed via condenser 120 to the control grids of the two indicator tubes. Shifting alternate sweeps of the time-base of the bearing indicator and suppressing alternate echo signals. A valve 75 in the master relay unit 24 supplies pulses to valve 78 (in unit 27) coupled to a low impedance valve 133. The cathode circuit of this valve supplies pulses to the suppressor grid of valve 93, Fig. 4, in time-base unit 26, where it shifts alternate sweeps of the trace, thereby separating the echo traces derived from the two forks of the wave guide. Another portion of the output of valve 133 is fed to the control grid of amplifier 59 (unit 18), where it causes the echo signals for the range tube to be suppressed on alternate sweeps of the time-base, thereby filling in the gaps created by signal deflections and preserving an unbroken contour of the spiral trace. This allows the point at which the signal flank leaves the spiral trace to be more accurately determined.